Wednesday, December 7, 2011

Global change and limitation

One foundation of ecology lies in the concept of state factors. Borrowed from soil science, state factors are the properties of ecosystems that are independent of the properties of the ecosystems [see earlier post]. The bedrock under a stand of plants is largely independent of whether a forest is there or we cut it down.

Ecosystems are not entirely deterministic from state factors and there are more proximal "interactive controls" like disturbance that are co-influenced by the vegetation. The probability of fire depends on what species are present as well as state factors like macroclimate.

One deficiency in our application of state factors and interactive controls has been to map the influence of state factors and interactive controls onto limitation. What factors and controls promote water-limitation over nutrient-limitation?

I've been trying to diagram this. Terry in his ecosystem book used a flow-control diagram to map the relative influences of state factors, interactive controls, and other controls on processes.

I've tried this approach for generating limitation and my diagrams come out looking like spaghetti. Or fettuccine. Some type of long, linear pasta. At least not fusilli thankfully.

The best I can come up with is a ternary diagram. In short, we want to show that drought, shade, and nutrient scarcity are all inversely related. And that a given global change factor promotes one or two stresses over the other. Precipitation promotes shade and nutrient scarcity over drought stress. Warmer temperatures promote drought and shade over nutrient scarcity. Disturbances reduce resource stress overall (inset).

There are dependencies for the diagram, e.g. chronic vs. catastrophic fire or scarcity of N vs. P.

Still I think this encapsulates the concepts we have about how global change factors alter limitation.

Mapping out other specific state factors is still a challenge. I get more spaghetti diagrams when I do this. Well, diagrams that look like I spilled dried spaghetti.